The Tick’s Pincher Offensive

Q. Why do I suffer more pain and itching, and for longer, after a tick bite than after a mosquito sting?

A. Despite the diseases they may carry, most tick bites are harmless, medical experts agree, while many mosquito bites inject anticoagulants that cause distressing immune-system reactions, including swelling and itching.

But there are exceptions in the tick world that can seriously wound their human hosts, and some do it by stealth, hiding their presence as long as they can.

Researchers have found that all ticks seek to set off a hemorrhage in the skin to form the kind of blood pool that is ideal for their meal, and some can leave considerable damage behind. They break capillaries and small blood vessels while probing for blood.

Some fast-feeding soft ticks cause the carnage with their larger mouth parts, penetrating the skin deeply and repeatedly.

Many species of ticks, especially hard ticks, use a kind of chemical warfare to let them feed longer at one site. Some of the many components of their saliva suppress the body’s normal inflammatory reaction to a bite. Other parts of their chemical arsenal prevent the host’s blood from clotting, which would interfere with feeding, and also suppress healing processes. These ticks may stay attached for several days or even weeks, with females sometimes absorbing 100 times their original body weight in blood. question@nytimes.com

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